Synthesis of ANSA-metallocene catalysts

ABSTRACT

A process of preparing in high yield ansa-metallocene complexes and rac-ansa-metallocene complexes by reacting an ansa-bis-cyclopentadiene compound with a metal amide complex.

GRANT REFERENCE

The invention here set forth was partially funded by the NationalScience Foundation Grant #CHE90-22700 Amend 02 and the government mayhave certain rights in the invention. The invention was also partiallyfunded by the Department of Energy Grant No. DE-FG 02-88ER13935.

BACKGROUND OF THE INVENTION

This invention relates to the field, now well established, of use ofansa-metallocenes as catalysts. They are particularly useful ascatalysts for the polymerization of ethylene and alpha olefins such aspropylene.

Conventional heterogeneous catalysts such as Ziegler-Natta systems havea variety of active sites, only some of which are stereo-specific.Obtaining a polymer with specific properties can involve a considerableamount of trial and error in order to find the best combination ofcatalyst, co-catalyst and stereo-regulator. In contrast, however, theactive polymerization site in a metallocene catalyst is well defined,and can be modified in a straightforward manner via modification by thecyclopentadienyl ligands, enabling the structure of the polymer to becontrolled with far greater precision.

A simple metallocene catalyst for polymerizing ethylene is (C₅ H₅)₂ZrCl₂ which consists of a zirconium atom bound to two chlorine atoms andtwo cyclopentadienyl rings, and which is activated by co-catalysts suchas methylaluminoxane (MAO). During the 1980's, ansa or bridgedmetallocenes, in which the cyclopentadienyl rings are linked by achemical bridge, were found to be particularly useful for thepolymerization of olefins. In particular, ansa-metallocene complexes,when used in combination with a co-catalyst such as methylaluminoxane(MAO), polymerize propylene to highly isotactic polypropylene, highlysyndiotactic polypropylene, or atactic polypropylene, depending on thestructure of the ansa-metallocene used.

As is well known, isotactic polymers have each pendant group attached tothe backbone in the same orientation, whereas in syndiotactic polymers,these groups alternate in their orientations and atactic polymers have arandom arrangement of the groups along the backbone. Since thestereochemistry of the polymer has a great effect on its properties, itis desirable to control this feature. Chiral, C₂ -symmetricansa-metallocenes produce isotactic polypropylene.

While the greatest area of potential use for ansa-metallocene catalystscurrently is for polymerization of olefins, such as ethylene andpropylene, they also have significant uses as catalysts or catalystprecursors for other reactions where stereo-selectivity is important.

The utility of ansa-metallocene complexes as catalysts for olefinpolymerization and other reactions has created a high demand for apractical synthesis of ansa-metallocene compounds.

In spite of this demand, current procedures for the synthesis of Group 4(Ti,Zr,Hf) ansa-metallocenes require the use ofansa-bis-cyclopentadienyl dianion reagents and are hampered by lowyields and tedious isomer separation and purification steps. Some ofthese problems have been discussed in Ellis, W. W.; Hollis, T. K.;Odenkirk, W., Whelan, J.; Ostrander, R.; Rheingold, A. L.; Bosnich, B.Organometallics 1993, 12, 4391. In particular, the synthesis of chiralC₂ symmetric ansa-metallocenes typically produces mixtures of desiredrac (racemic) and undesired meso isomers. A typical synthesis of anansa-metallocene complex is shown in equation 1 below: ##STR1##

This equation is typical of the process as shown in the art. See forexample Spaleck, W.; Kuber, F., Winter, A.; Rohrman, J.; Bachmann, B.;Antberg, M.; Dolle, V.; Paulus, E. F. Organometallics 1994, 13, 954.Stehling, U.; Diebold, J.; Kirsten, R.; Roll, W.; Brintzinger, H. H.;Jungling, S.; Mulhaupt, R.; Langhauser, F. Organometallics 1994, 13,964. Halterman, R. L. Chem. Rev. 1992, 92, 965. See also, for example,U.S. Pat. No. 5,145,819, U.S. Pat. No. 5,268,495, and EPA 0-530-908-A1.

By way of further example, an important chiral Group 4 ansa-metalloceneis rac-(EBI)ZrCl2 (EBI=ethylene-1,2-bis(1-indenyl) which is currentlyprepared from ZrCl₄ and the dianion of the EBI ligand (Halterman, R. L.Chem. Rev. 1992, 92, 965). Brintzinger (Wild, F. R. W. P.; Wasiucionek,M.; Huttner, G., Brintzinger, H. H. J. Organomet. Chem. 1985, 288, 63)and Collins (Collins, S.; Kuntz, B. A.; Hong, Y. J. Org. Chem. 1989, 54,4154; Collins, S.; Kuntz, B. A.; Taylor, N. J.; Ward, D. G. J.Organomet. Chem. 1988, 342, 21) used (EBI)Li₂ and reported low, variableyields (20-50%) of rac-(EBI)ZrCl₂. Buchwald employed (EBI)K₂ andobtained (EBI)ZrCl₂ in a rac/meso ratio of 2/1 in 70% yield. Grossman,R. B.; Doyle, R. A.; Buchwald, S. L. Organometallics 1991, 10, 1501. Ingeneral, current synthetic procedures produce the desired racansa-metallocenes in 10%-30% yield after tedious separation andpurification steps, and even then separation of the rac from the mesoproducts is not always possible.

Lappert et al. (Chandra, G.; Lappert, M. F. J. Chem Soc. (A) 1968, 1940)reported that certain Group 4 metallocene complexes are formed by thereaction of Group 4 metal amide complexes with cyclopentadienecompounds. However, this reaction yields only mono-cyclopentadienylproducts when the metal is titanium, or when the cyclopentadienecompound is indene. This was ascribed to steric hindrance whichdisfavors addition of the second cyclopentadienyl ligand when the metalis small (titanium) or the cyclopentadienyl ligand is bulky (indenyl).Hefner, et al., also (U.S. Pat. No. 5,194,532) discusses the preparationof (indenyl)Ti(NMe₂)₃ by reaction of indene and Ti(NMe₂)₄.Ansa-metallocene complexes are not discussed in the Lappert or Hefnerreferences.

There is, therefore, a need for a process which would produceansa-metallocene complexes in high yield. Additionally, there is a needfor a process which would produce rac ansa-metallocenes in high yieldwithout contamination by the meso isomer, since the rac isomer is mostuseful in stereoselective catalysis. The present invention has as itsprimary objectives the fulfillment of these needs.

It is another objective of the present invention to prepare racansa-metallocenes by means of a single step process, in most instancesin yields of 70% or higher, without the use of ansa-bis-cyclopentadienyldianion reagents.

SUMMARY OF THE INVENTION

The process of preparing rac ansa-metallocene complexes in high yield byreacting an ansa-bis-cyclopentadiene, indene, fluorene, or substitutedderivative thereof with a metal amide complex wherein the metal is aGroup 4 metal, preferably zirconium, and R and R' (eq. 2) are preferablyhydrogen or C₁ to C₂₀ hydrocarbyl radicals, and more preferably C₁ to C₄alkyl and most preferably methyl.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, ansa-metallocene complexes of general formula##STR2## are prepared by reaction of metal amide complexes withansa-bis-cyclopentadiene compounds as illustrated in eq. 2. ##STR3##

R and R' represent hydrogen or hydrocarbyl radicals having from 1 to 20carbon atoms, preferably from 1 to 4 carbon atoms. R and R' may also besilyl radicals SiR₃. R and R' may be linked.

Cp independently in each occurrence is a cyclopentadienyl, indenyl,fluorenyl or related group that can π-bond to the metal, or ahydrocarbyl, alkyl, aryl, silyl, halo, halohydrocarbyl,hydrocarbylmetalloid, or halohydrocarbylmetalloid substituted derivativethereof. Cp may contain up to 75 nonhydrogen atoms.

X may be any bridging or ansa group that is used to link the Cp groups,including, for example, silylene (--SIR₂ --), benzo (C₆ H₄) orsubstituted benzo, methylene (--CH₂) or substituted methylene, ethylene(--CH₂ CH₂ --), or substituted ethylene bridges.

M represents the metal used and is usually a Group 4 metal selected fromthe group consisting of titanium, zirconium and hafnium, but may also bea Group 3 (Sc,Y,La), Group 5 (V,Nb,Ta), Lanthanide or Actinide metal.Preferably it is a Group 4 metal, and most preferably it is zirconium.

n is a whole number and is from 3 to 5. When M is a Group 4 metal or anActinide "n" is 4, when M is a Group 3 or Lanthanide metal "n" is 3, andwhen M is a Group 5 metal "n" is 5.

In particular, the rac isomers of chiral C₂ -symmetric ansa-metallocenesare prepared in high yield. An example is the reaction of Zr(NMe₂)₄ with(EBI)H₂, shown below (eq. 3). This reaction provides an efficient, highyield synthesis of pure rac-(EBI)Zr(NMe₂)₂, which can easily beconverted to rac-(EBI)ZrCl₂ and related derivatives. ##STR4##

The process of making each starting material for this reaction is known.In particular, the synthesis of ansa-bis-cyclopentadienes such as(EBI)H₂ is described in Halterman, R. L. Chem. Rev. 1992, 92, 965, andreferences therein.

The metal amide complexes M(NR'R')₄ can be prepared by reacting thecorresponding metal tetrahalide complex such as zirconium tetrachloridewith an appropriate lithium amide, see D. C. Bradley and I. M. Thomas,Proc. Chem. Soc., 1959, 225; J. Chem. Soc. 1960, 3857. As earlierindicated, it is preferred that R and R' be hydrogen or C₁ to C₂₀hydrocarbyl radicals and preferably C₁ to C₄. Methyl is the mostpreferred and is illustrated in eq. 3.

The reaction between the ansa-bis-cyclopentadiene and the metal amidecan take place at any temperature from ambient, i.e., about 25° C. up to250° C., preferably within the range of 80° C. to 125° C. At 100° C. thereaction is typically complete in less than 24 hours, and perhaps as fewas 3 to 5 hours. The reaction is unaffected by room light and appears tobe reversible.

The dimethylamine produced as a by-product in eq. 3 is gaseous. It ispreferred that this not be completely swept away by gas flushing duringthe reaction as it is believed that it may catalyze the conversion ofinitially formed meso product to the desired rac product, therefore,ultimately yielding a higher ratio of rac/meso. This is believed thecase because it has been observed that when the reaction flask isflushed with inert gas during the reaction, the yield of desired racproduct decreases significantly.

While the use of metal amide complexes as starting materials isdiscussed above, if the NRR' groups are replaced with PRR' or SR groups,it is expected that equivalent results will be achieved. Likewise, amidecomplexes of the Group 3 metals, (Sc,Y,La), Group 5 metals (V,Nb,Ta) andthe Actinides and Lanthanides may also be used, and it is expected thatequivalent results will be achieved.

It is also expected that use of chiral, enantiomerically enriched metalamide complexes in equation 2 will allow the synthesis ofenantiomerically enriched ansa-metallocenes.

The reaction desirably is conducted in the presence of a nonaqueous,nonalcoholic, solvent that at least partially dissolves one of thereactants. Typical of such solvents are hydrocarbons such as benzene,toluene, and hexane, simple ethers, chlorinated hydrocarbons,acetonitrile, tetrahydrofuran, etc.

It is believed that the metallocene amido complexes which are producedin eq. 2 may, when activated by a suitable cocatalyst, be used ascatalysts in many applications. Alternatively, the metallocene amidocomplexes which are produced in eq. 2 may be converted to the morecommonly used metallocene chloride complexes by a simple protonationreaction as described in Hughes, A. K.; Meetsma, A.; Teuben, J. H.,Organometallics 1993, 12, 1936.

The following examples are offered to further illustrate but not limitthe process of the present invention.

EXAMPLE

The ansa-metallocene rac-(EBI)Zr(NMe₂)₂ has been prepared in high yieldfrom Zr(NMe₂)₄ and (EBI)H₂ (eq. 3). In a typical reaction, under N₂atmosphere, Zr(NMe₂)₄ (0.50 g, 1.9 mmol) and (EBI)H₂ (0.48 g, 1.9 mmol)were placed in a Schlenk vessel containing a Teflon stir bar. Toluene(50 ml) was added. The reaction mixture was stirred and heated to 100°C. for 17 hours. During this period, the HNMe₂ co-product was allowed toescape freely (via an oil bubbler) from the reaction vessel. Removal ofsolvent under reduced pressure afforded an orange solid which was shownby ¹ H NMR to be (EBI)Zr(NMe₂)₂ in a rac/meso ration of 10/1, in 90%yield. Recrystallization from hexane afforded pure rac-(EBI)Zr(NMe₂)₂ in73% isolated yield (0.59 g). The rac-(EBI)Zr(NMe₂)₂ was characterized by¹ H and ¹³ C NMR, elemental analysis, and an X-ray crystal structuredetermination.

It was also shown that rac-(EBI)Zr(NMe₂)₂ reacts with two equivalents ofMe₂ NH.HCl to give rac-(EBI)ZrCl₂ in high isolated yield (eq.4). In atypical reaction, under N₂ atmosphere, a solution of Me₂ NH.HCl (0.093g, 1.14 mmol) in CH₂ Cl₂ (20 ml) was added dropwise to a stirredsolution of rac-(EBI)Zr(NMe₂)₂ (0.25 g, 0.57 mmol) at -78° C. Theresulting clear, yellow solution was stirred at room temperature for 30mins. The solvent was removed under reduced pressure and the resultingsolid was washed with hexane (15 ml) and extracted with toluene (70 ml).Removal of the solvent from the toluene extract under reduced pressuregave pure rac-(EBI)ZrCl₂ in 92% isolated yield (0.22 g). (Eq. 4)##STR5##

The following additional examples were run using the basic synthesisshown in Example 1 and are presented here for succinctness in tableform.

                                      TABLE    __________________________________________________________________________    Synthesis of rac-(EBI)Zr(NMe.sub.2).sub.2 in high yield.                                          % isolated                                     rac/meso                                          rac-                 reaction   (EBI)Zr(NMe.sub.2).sub.2                                     ratio of                                          (EBI)Zr(NMe.sub.2).sub.2    Example   temp                 time system                            as % of crude                                     crude                                          (crystallized    No.  solvent              (°C.)                 (hours)                      used  product  product                                          from)    __________________________________________________________________________    2    toluene              100                 48   N.sub.2                            90       1/1  25                      purge.sup.(a)       (toluene)    3    toluene              100                 26   partial N.sub.2                            80       4/1  --                      purge.sup.(b)    4    toluene              100                 17   N.sub.2                            90       1/1  --                      purge.sup.(a)    5    chloro-              125                 17   open.sup.(c)                            90       9/1  70         benzene                          (hexane)    6    toluene              100                 117  open.sup.(c)                            <60      60/1 --    7    toluene              100                 12   pressure                            85       10/1 75                      release.sup.(d)     (toluene)    8    toluene              100                 18   closed.sup.(e)                            50       1/1  --    9    toluene              100                 17   open.sup.(c)                            90       13/1 68                                          (toluene)    10   toluene              100                 18   open  90       13/1 --                      dark.sup.(f)    11   THF   67                 20   open.sup.(c)                            50       2/1  --    __________________________________________________________________________     .sup.(a) N.sub.2 bubbled through reaction solution to drive off HNMe.sub.     as it is formed     .sup.(b) N.sub.2 bubbled through reaction solution only for part of     reaction time     .sup.(c) HNMe.sub.2 allowed to escape freely (via an oil bubbler) from     reaction vessel     .sup.(d) HNMe.sub.2 allowed to escape from reaction vessel via a mercury     bubbler     .sup.(e) closed system, HNMe.sub.2 is retained in reaction vessel     .sup.(f) as for (c) except reaction vessel wrapped in aluminum foil to     exclude light

It can therefore be seen that the invention accomplishes all of itsstated objectives in that ansa-metallocenes were prepared in pure racform in high yields without the use of ansa-bis-cyclopentadienyl dianionreagents. The yields are substantially higher than the traditional priorart yields of 10% to 30%.

What is claimed is:
 1. A process of synthesizing in high yieldansa-metallocene complexes of the formula: ##STR6## wherein Cpindependently and in each occurrence is cyclopentadienyl, indenyl, orfluorenyl, or a related group that can π-bond to the metal, or ahydrocarbyl, alkyl, aryl, silyl, halo, halohydrocarbyl,hydrocarbylmetalloid, or halohydrocarbylmetalloid substituted derivativeof said cyclopentadienyl, indenyl, fluorenyl or related group, X is abridging group which links the Cp groups, M is a metal selected from thegroup consisting of Group 3, 4, and 5 metals, R and R' are the same ordifferent and are each hydrogen or hydrocarbyl radicals of from C₁ toC₂₀, or silyl radicals, and n is from 3 to 5, said process comprising:reacting an ansa-bis Cp compound of the formula HCp--X--CpH where Cp andX are as above defined with a metal amide complex to provide a highyield of ansa-metallocene complex.
 2. The process of claim 1 wherein theGroup 4 metal is selected from the group consisting of zirconium,titanium and hafnium.
 3. The process of claim 2 wherein the metal iszirconium.
 4. The process of claim 1 wherein R and R' are independentlyC₁ to C₄ alkyl.
 5. The process of claim 4 wherein R and R' are methyland the gaseous byproduct dimethylamine is not swept away from thereaction as it is produced.
 6. The process of claim 1 wherein saidprocess is conducted at a temperature ranging from 25° C. to 250° C. 7.The process of claim 1 wherein said process is conducted at atemperature ranging from 80° C. to 125° C.
 8. The process of claim 1wherein the reaction is conducted in the presence of a nonaqueous,nonalcoholic organic solvent.
 9. The process of claim 8 wherein thesolvent is selected from the group consisting of hydrocarbons, toluene,ethers, chlorinated hydrocarbons and tetrahydrofuran.
 10. The process ofclaim 1 where X is ethylene and Cp is indenyl.
 11. A process ofsynthesizing in high yield ansa-metallocene complexes of the formula:##STR7## wherein Cp independently and in each occurrence iscyclopentadienyl, indenyl, or fluorenyl, or a related group that canπ-bond to the metal, or a hydrocarbyl, alkyl, aryl, silyl, halo,halohydrocarbyl, hydrocarbylmetalloid, or halohydrocarbylmetalloidsubstituted derivative of said cyclopentadienyl indenyl, fluorenyl orrelated group, X is a bridging group which links the Cp groups, M is ametal selected from the group consisting of Group 3, 4, and 5 metals, Rand R' are the same or different and are each hydrogen or hydrocarbylradicals of from C₁ to C₂₀, or silyl radicals, and n is from 3 to 5,said process comprising: reacting an ansa-bis Cp compound of the formulaHCp--X--CpH where Cp and X are as above defined with a metal amidecomplex to provide a high yield of ansa-metallocene complex; andthereafter,isolating the ansa-metallocene complex from the reactionmixture.
 12. The process of claim 11 wherein the metal is a Group 4metal and n is
 4. 13. The process of claim 12 wherein the metal iszirconium and n is
 4. 14. The process of claim 11 wherein R and R' areboth methyl.
 15. The process of claim 14 wherein X is an ethylene moietyand Cp is indenyl.
 16. The process of claim 11 wherein R and R' aremethyl and the gaseous byproduct dimethylamine is not swept away fromthe reaction as it is produced.
 17. A process of synthesizing in highyield rac ansa-metallocene complexes of the formula: ##STR8## wherein Cpindependently and in each occurrence is a hydrocarbyl, alkyl, aryl,silyl, halo, halohydrocarbyl, hydrocarbylmetalloid, orhalohydrocarbylmetalloid substituted cyclopentadienyl, an indenyl, afluorenyl, or a related group that can π-bond to the metal, or ahydrocarbyl, alkyl, aryl, silyl, halo, halohydrocarbyl,hydrocarbylmetalloid, or halohydrocarbylmetalloid substituted derivativeof said indenyl, fluorenyl, or related group, X is a bridging groupwhich links the Cp groups, M is a metal selected from the groupconsisting of Group 3, 4, and 5 metals, R and R' are the same ordifferent or linked and are each hydrogen or hydrocarbyl radicals offrom C₁ to C₂₀, or silyl radicals, and n is from 3 to 5, said processcomprising: reacting a hydrocarbyl, alkyl, aryl, silyl, halo,halohydrocarbyl, hydrocarbylmetalloid, or halohydrocarbylmetalloidsubstituted ansa-bis-cyclopentadiene, or an ansa-bis-indene, or anansa-bis-fluorene or a related group that can π-bond to the metal, or ahydrocarbyl, alkyl, aryl, silyl, halo, halohydrocarbyl,hydrocarbylmetalloid, or halohydrocarbylmetalloid substituted derivativeof said ansa-bis-indene, ansa-bis-fluorene or related group, with ametal amide complex to provide a high yield of rac ansa-metallocenecomplex.
 18. The process of claim 17 which includes as an additionalstep isolating the rac ansa-metallocene complex.
 19. The process ofclaim 18 wherein X is ethylene and Cp is indenyl.
 20. The process ofclaim 1 which includes a step of converting the ansa-metallocene amidocomplex to an ansa-metallocene chloride complex.